I have a 98 Mustang GT that has been PI swapped. (Heads, Cams, Exc.)

The car has 82,000 miles on it and has ran very strong.

Lately I have been experiencing some issues out of it. The car is starting to run really lean, and it will even smoke a little when the weather is hot or when the car warms up. Also when it idles down it seems like the car is trying to kill the motor. The rpm will jump from like 800 rpm to 600 and pull itself back up when the motor tempature is in the middle. The car runs perfect when the motor is cool, and the cold weather has helped it alot lately. The car has a SCT Tune, but I misplaced the handheld at a car show. I have checked the oil to see if it was burning alot of oil and it was normal, I run royal purple in my car so know junk goes through it.

Thank you all for viewing, I hope I can get some help.

 

Bump.

 

Maybe bad IAC? They're fairly cheap to replace, so might be worth a try. You didn't mention if your check engine light is on, if so get it checked for a better diagnosis than my guessing.

 

^^ I second that. Most "common" idle issues (that include surging of the rpms at idle, surging under load (like with the A/C on)) is due to a faulty IAC. A quick-fix is to spray it with some form of cleaner. If that doesn't work, you need to replace it. Easy process, cost about $100.